This invention relates to plunger lubricants and their use in die casting processes.
Although die casting processes have been known for many years, problems still exist. One of the continuing problems relates to area of plunger lubricants and other lubricants necessary for the efficient and cost effective manufacture of die cast metal parts. Known lubricants have a variety of environmental, safety and housekeeping issues.
A die casting apparatus generally comprises a die and a shot sleeve. The molten metal to be cast is introduced into the shot sleeve. A plunger axially extends into the shot sleeve to push the molten metal into the die. The shot sleeve and plunger require lubrication because the molten metal can solder itself to the shot sleeve and/or the plunger and because of the plunger can generate significant amounts of additional heat from friction as it rubs against the shot sleeve. Furthermore, lubricants help prevent the plunger from rubbing unevenly against the inside wall of the shot sleeve. The uneven rubbing prevents a smooth plunger movement which may result in a sub par cast, which must be discarded. The uneven rubbing also leads to significantly increased wear and tear on the plunger and the shot sleeve, which cause increase down time, repair costs and eventually will necessitate the replacement of the plunger.
Various kinds of lubricants have been utilized in the past with less than satisfactory results. Oil-based lubricants are disfavored because they tend to smoke and degrade when they come in contact with the molten metal or the shot sleeve that is hot from repeated use. Oil-based lubricants required large amounts of warehouse space because they are bulky. Furthermore, oil-based lubricants present a slip-and-fall hazard if spattered on the floor.
Water-based lubricants avoid the smoking and degrading of oil based lubricants, but suffer their own drawbacks. The major draw back is that the water carrier must be completely evaporated prior to the introduction of the molten metal because a violent reaction could result if the molten metal comes into contact with water. Water-based lubricants are typically sprayed into the shot sleeve through the use of compressed air. The noise of the compressed air and the machinery used to produce the compressed air requires that soundproofing structures be utilized with the consonant added expense. In addition, liquid lubricants require pumps and tubes which are susceptible to mechanical failure from extended periods of use. Water-based lubricants often include particulate materials such as graphite or other inorganic particles which tend to coagulate at or in the spray nozzle used to apply the lubricant. This decreases the reliability of the machinery used to apply the lubricant because the nozzle must be periodically cleaned. Furthermore, partial lubrication of the shot sleeve can result from a partially blocked nozzle, thus leading to uneven rubbing of the plunger in the shot sleeve and its attendant problems. Water-based lubricants also required large amounts of warehouse space because they are bulky.
Other kinds of lubricants including solids in the form of pellets, powders and flakes have been used. These suffer some of the same defects as water-based lubricants. Known pelleted lubricants tend to bounce on the floor during application and create a slip-and-fall hazard. Powder and flake lubricants may require complicated additional machinery to effect their use, thus making their utilization more expensive and labor intensive. Furthermore, the lubricant materials may be more expensive than water-based materials because of their limited availability.
In addition, all known lubricants suffer from serious cleanliness problems. Known liquid lubricants tend to spatter excessively when applied. Known powdered lubricant tend to create dusty working conditions. In either case, significant amounts of time, energy and money must be expended to keep the work area clean and safe because spattered lubricants interfere with the switch out of empty lubricant containers, create unpleasant working conditions, and may be a fire hazard.
Accordingly, the inventor has recognized a need for improve plunger lubricants, and associated processes of applying those lubricants, which overcome one or more of these drawbacks.
The present invention relates to a die casting machine which includes a dispenser that causes a plunger lubricant to undergo a phase change. The dispenser also dispenses the plunger lubricant. The present invention also relates to a method of lubricating a die casting machine which involves effecting a phase change in the plunger lubricant prior to dispensing the plunger lubricant. The present invention also relates to a plunger lubricant blank which under goes a phase change in the dispenser.